Computers are now used to store massive amounts of information. In order to locate particular information of interest, powerful and intuitive search mechanisms have been created. For example, the World Wide Web portion of the Internet has grown exponentially since the late 1980's when the World Wide Web was first introduced. Early in the history of the World Wide Web, directories of web sites were used to guide users to web sites of interest. One of the most famous early web site directories was “Jerry's Guide to the World Wide Web” which was later renamed “Yahoo!”. However, the rapid real-time growth of the Internet quickly made World Wide Web directories unmanageable and prone to being out of date. Internet search engines such as Lycos, Alta Vista, and Google became the new method finding web sites on the Internet. Internet search engines allow a user to enter a few keywords related to the topic of interest and return with a large set of search results that contain the keywords entered by the user.
Internet search engines operate by “crawling” the World Wide Web to learn about new web pages and then create a searchable index of all the web pages that were visited. When a user enters a set of keywords, the search engine returns a set of web pages that contain the keywords entered by the user. However, most queries entered by search engine users will map to thousands or even hundreds of thousands of results that contain the matching keywords. This information overload is not desired by the user. Thus, the real key to building a very good search engine and thereby a good online listing system (e.g., eBay) is to sort the results by some type of relevancy measure. In this manner, the user of an internet search engine may quickly find desired content.